The present invention relates to a color filter to be used for a flat display, such as a liquid crystal display, a plasma display, a field emission display, and an electro luminescence panel, a pigment dispersion composition used for the production thereof, and a production method of the pigment dispersion composition.
Conventionally, a color filter having a coloring layer formed, using a composition with a pigment dispersed has been used as a color separation filter for a flat display, such as a liquid crystal display (LCD), a plasma display (PDP), a field emission display (FED), and an electro luminescence panel (EL) For example, in the case of the LCD, a color filter comprising a coloring layer with an organic pigment dispersed and contained, and a black matrix with a black pigment dispersed and contained is used.
As a pigment dispersion composition for a color filter, following compositions have been used conventionally as ultraviolet ray curing type compositions, and thermosetting type compositions.
(Ultraviolet Ray Curing Type)
pigment
pigment dispersing agent
binder resin
polyfunctional monomer
photo polymerization initiator
resin having an epoxy group (as needed) (Thermosetting Type)
pigment
pigment dispersing agent
binder resin
resin having an epoxy group
hardening accelerator
Since a high transmittance and a low light scattering property are required for a color filter of a flat display, a pigment dispersion composition for a color filter should maintain a stable state by dispersion a pigment to a primary particle. A pigment dispersing agent to be used for the above-mentioned pigment dispersion compositions is for dispersing a pigment to a primary particle for stabilizing the state thereof. As examples thereof, those mainly having a pigment dispersing function (Japanese Patent Application Laid Open Nos. 5-611196, 5-247354, 10-300919, or the like), and those having both pigment dispersing property and alkaline developing property (Japanese Patent No. 2,665,696, Japanese Patent Application Laid Open Nos. 10-46042, 11-33383, or the like) are known. These pigment dispersing agents have the kind of a contained functional group, and the kind of a monomer limited. In either of the pigment dispersing agents, use of a binder resin having a reactivity or an alkaline developing property is the premise thereof.
As a binder resin having an alkaline developing property, a binder resin with a higher-order structure comprising a block having an acid group and a block without an acid group defined is disclosed (Japanese Patent Application Laid Open No. 5-273411).
Moreover, as a binder resin having a reactivity and an alkaline developing property, one having a reactive group introduced using an unsaturated group and an alicyclic epoxy compound (Japanese Patent Application Laid Open No. 8-262221), one having the introduction position of an ethylenically unsaturated group defined (Japanese Patent Application Laid Open No. 5-19467), and the like are disclosed.
In contrast, as a conventional production method of a pigment dispersion composition, a method of mechanically kneading a pigment, a pigment dispersing agent, a solvent and a binder resin (Japanese Patent Application Laid Open No. 7-13016), a method of mixing a dispersion material of a 0.3 xcexcm or less average particle size produced by processing a pigment, a low molecular weight binder, a solvent, and a dispersing agent with a dispersing machine such as a bead mill, and a three roll mill, and a photosensitive resin composition containing a high molecular weight binder (Japanese Patent Application Laid Open No. 9-134004), and the like are disclosed.
In the case of dispersing a pigment to the primary particle state only by a pigment dispersing agent in a pigment dispersion composition for a color filter, although it is stable as a pigment dispersing agent, a problem of the pigment aggregation is involved due to insufficiency of the compatibility of the other resin components such as a binder resin, or the like with the pigment dispersing agent, and a problem is involved in that the residue amount after development in a photolithography step is large due to increase of the pigment dispersing agent amount contained in the pigment dispersion composition, and it gives an adverse effect as an impurity on the display reliability of the display, or the patterning performance is deteriorated.
In order to solve the problems, a binder resin having a pigment dispersing function is used. Since such a binder resin is adsorbed on the pigment surface, the addition amount of the pigment dispersing agent can be made smaller, and thus the residue amount after development in a photolithography step can be reduced.
However, in the case of using such a binder resin having a pigment dispersing function, a problem of deterioration of the dispersion stability is involved due to reduction of the addition amount of the pigment dispersing agent. Moreover, since both of a binder resin having a bonding function inherent to a binder resin, and a binder resin having a pigment dispersing function need to be used together, problems are involved in that the bonding function by the binder resin is deteriorated relatively, and in that the compatibility of the two binder resins to be used should be taken into consideration and thus the resin design is difficult.
Moreover, according to the production method of a pigment dispersion composition described above, problems are involved in that the particle size distribution of a pigment dispersion material processed with a bead mill is made larger, and in that the process time for obtaining a desired particle size distribution is long. Furthermore, problems are involved in that the temperature can be raised due to continuation of the dispersing process so as to raise the viscosity of the pigment dispersion material so that the viscosity of the final composition cannot be set at a desired viscosity, or in that an excessive pressure amount is generated inside the dispersing machine so that the device is stopped or damaged.
Moreover, even in the case the particle size of the pigment dispersion material dispersed by a beadmill is small, the mixing operation of the resin component and the pigment dispersion material is executed unevenly only by dispersing with a roll mill after mixing with the other resin components by an ordinary agitating machine, and thus a problem is involved in that the resin and the pigment are separated, or a long time is needed for the dispersing operation.
In view of the above-mentioned circumstances, the present invention has been achieved. An object thereof is to provide a pigment dispersion composition for a color filter having the excellent pigment dispersing property and dispersion stability, good developing property and reactivity, and an extremely small residue generation amount after development, a production method capable of stably producing such a pigment dispersion composition, and a color filter for a display having a high transmittance and a low light scattering property.
In order to achieve the object, a pigment dispersion composition for a color filter according to the present invention contains at least a pigment, a pigment dispersing agent, a binder resin, a reactive compound, and a solvent, wherein the binder resin is a compound having a pigment adsorbing block containing a pigment adsorbing group and not containing a reactive group, and a reactive block containing a reactive group and not containing a pigment adsorbing group.
Moreover, a pigment dispersion composition for a color filter according to the present invention has the average particle size of the pigment of 0.15 xcexcm or less.
Furthermore, according to a pigment dispersion composition for a color filter of the present invention, the pigment adsorbing block is a trunk polymer with the pigment adsorbing group being at least one selected from the group consisting of a carboxymethyl group, a sulfonic group, a sulfuric acid group, a phosphonic acid group, a phosphoric acid group, an amino group, and a group containing an aromatic ring, and the reactive block is a branch polymer with a molecular weight in a range from 3,000 to 20,000, having at least a reactive group in a 3,000 to 20,000 molecular weight range from the bonding point with the pigment adsorbing block.
Moreover, according to a pigment dispersion composition for a color filter of the present invention, the binder resin molecular weight in the above-mentioned pigment dispersion composition is in a range from 10,000 to 50,000, and the reactive block has an unsaturated double bond in a reactive group as well as contains a carboxyl group, the reactive block further contains a hydroxyl group, the reactive compound is a photo reactive compound and/or a thermally reactive compound, having a polyfunctional monomer with an unsaturated double bond, or the reactive compound further contains an epoxy group.
Furthermore, according to a pigment dispersion composition for a color filter of the present invention, in the above-mentioned pigment dispersion composition, a polyvalent carboxylic acid group or an acid anhydride is further contained, the binder resin has an epoxy group as a reactive group of the reactive block, and the reactive compound is a photo reactive compound and/or a thermally reactive compound containing an epoxy group.
A production method of a pigment dispersion composition for a color filter according to the present invention is a method for producing the above-mentioned pigment dispersion composition for a color filter, wherein a pigment dispersion material of a 0.15 xcexcm or less average particle size produced by kneading a mixture of a pigment, a pigment dispersing agent, a binder resin, and a solvent by an annular type medium dispersing machine using ceramic beads of a 0.5 mm or less diameter, and a reactive composition containing a reactive compound and as needed a solvent, are mixed.
Moreover, according to a production method of a pigment dispersion composition for a color filter of the present invention, the mixing operation for the pigment dispersion material and the reactive composition comprises a step of mixing by a kneading machine having a plurality of rotation axes and a frame type blade, and a step of dispersing by a bead mill using ceramic beads of a 0.5 to 2 mm diameter, and further a dispersion step by a three rolls mill after the dispersion steps.
A color filter for a display according to the present invention comprises a supporting member, and a plurality of coloring layers formed on the supporting member by a predetermined pattern, wherein the coloring layers are formed with the above-mentioned pigment dispersion composition for a color filter.
Since a binder resin contained in a pigment dispersion composition according to the present invention sufficiently provides a function of adsorbing a pigment by a pigment adsorbing block thereof via a pigment adsorbing group, the pigment can be dispersed to a primary particle so that a reactive block can sufficiently perform a reactive function so as to bond with a reactive compound. Therefore, the pigment can be held stably in the state dispersed to the primary particle. Moreover, an annular type medium dispersing machine using ceramic beads of a 0.5 mm or less diameter can make the average particle size of the pigment dispersion material 0.15 xcexcm or less in the production stage. Since the pigment adsorbing block of the binder resin adsorbs the pigment in the pigment dispersion material as well as the reactive block of the binder resin can bond with the reactive compound in the mixing operation with a reactive compound, aggregation of the pigment, and separation of the pigment dispersion material and the reactive compound can be prevented.
As heretofore described in detail, according to the present invention, since a pigment dispersion composition containing at least a pigment, a pigment dispersing agent, a binder resin, a reactive compound, and a solvent is provided, and the binder resin is a compound having a pigment adsorbing block containing a pigment adsorbing group and not containing a reactive group, and a reactive block containing a reactive group and not containing a pigment adsorbing group, the pigment adsorbing block and the reactive block can sufficiently provide the function per each block. Since the pigment adsorbing block of the binder resin adsorbs a pigment via a pigment adsorbing group, the pigment can be dispersed to a primary particle so that the pigment can be held stably in the dispersed state. Moreover, since the reactive block can be bonded with the reactive compound, the binder resin bonding function can be provided sufficiently. Thereby, a good compatibility can be obtained among the pigment, the binder resin, and the reactive compound. Moreover, since the content of the pigment dispersing agent can be reduced so that the resin component content is increased relatively, the residue amount after development in the photolithography step can be reduced so as to improve the film forming property (sensitivity, developing property) . Furthermore, the strength, the heat resistance, and the chemical resistance of the film after formation can be improved as well as a high display reliability can be realized. Moreover, an annular type medium dispersing machine using ceramic beads of a 0.5 mm or less diameter can make the average particle size of the pigment dispersion material 0.15 xcexcm or less in the production stage. Since the pigment adsorbing block of the binder resin adsorbs the pigment in the pigment dispersion material as well as the reactive block of the binder resin can bond with the reactive compound, aggregation of the pigment, and separation of the pigment dispersion material and the reactive composition can be prevented in the mixing operation of the pigment dispersion material and the reactive composition. A coloring layer formed using a pigment dispersion composition according to the present invention provides a color filter for a flat display having a small average particle size of the contained pigment, a high transmittance and a low light scattering property.